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1Center for Terahertz waves and College of Precision Instrument and Optoelectronics Engineering, Tianjin University and the Key Laboratory of Optoelectronics Information and Technology (Ministry of Education), Tianjin 300072, China

2Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia

Abstract

Dielectric metasurfaces have achieved great success in realizing high-efficiency wavefront control in the optical and infrared ranges. Here, we experimentally demonstrate several efficient, polarization-independent, all-silicon dielectric metasurfaces in the terahertz regime. The metasurfaces are composed of cylindrical silicon pillars on a silicon substrate, which can be easily fabricated using etching technology for semiconductors. By locally tailoring the diameter of the pillars, full control over abrupt phase changes can be achieved. To show the controlling ability of the metasurfaces, an anomalous deflector, three Bessel beam generators, and three vortex beam generators are fabricated and characterized. We also show that the proposed metasurfaces can be easily combined to form composite devices with extended functionalities. The proposed controlling method has promising applications in developing low-loss, ultra-compact spatial terahertz modulation devices.

Figures (5)

Schematic of the silicon pillar structure and the simulated results of the selected eight silicon pillars. (a) Schematic of a silicon pillar in the uniform hexagonal lattice on a silicon substrate. The lattice constant p=100μm, and the pillar height h=150μm. (b) Simulated phase shifts and transmission amplitudes of the eight selected silicon pillars with different diameters d at 1.0 THz. The diameters corresponding to the pillars in the upper row from number 1–8 are d=20, 44.5, 53.5, 60, 66.5, 73, 79.5, and 88.5 μm, respectively. (c) Simulated side views (x–z planes) of the magnetic energy density distributions in four silicon pillars among the eight selections with d=44.5, 60, 73, and 88.5 μm, respectively, at 1.0 THz. An x-polarized plane wave with magnetic energy density of 1 is normally incident on the silicon pillars from the bottom (substrate side).

SEM image of the B0 generator and experimental results of the B0, B1, and B2 generators. (a) SEM image of part of the fabricated B0 generator. (b) Schematic of FNSTM. (c, f, i) Measured normalized intensity distributions of the B0, B1, and B2 generators in the x–z planes, respectively, at 1.0 THz. (d, g, j) The corresponding measured normalized intensity distributions in the x–y planes. (e, h, k) The corresponding measured phase distributions in the x–y planes. The intensity and phase distributions in the x–y planes of the B0, B1, and B2 generators are detected at 5, 5, and 6 mm away from the generators, respectively. The scanning step is 0.25 mm.

SEM images and experimental results of the V1, V2, and V4 generators. (a, d, g) SEM images of part of the fabricated V1, V2, and V4 generators, respectively. The different color shades represent different phase sections schematically, as indicated by (a). (b, e, h) Measured phase distributions of the output electric fields of the V1, V2, and V4 generators, respectively, at 1.0 THz. (c, f, i) The corresponding measured normalized intensity distributions. All of the distributions are detected at a distance of 10 mm from the generators. The scanning step is 0.4 mm.

Schematic of the CB1 generator and the corresponding experimental results. (a) Schematic of the CB1 composite beam generator composed of the V1 and B0 generators. The terahertz beam is incident from the V1 generator. (b) Measured normalized intensity distributions of the CB1 generator in the x–z plane at 1.0 THz. (c, d) The corresponding measured normalized intensity and phase distributions in the x–y plane, respectively. The intensity and phase distributions in the x–y plane are detected at 5 mm away from the generator. The scanning step is 0.25 mm.